Fracturing with field gas

Fuel to power a fracture stimulation job can be a major expense in today’s shale-dominated market, where a single well may require more than two dozen fracture stages to achieve maximum production and recovery. A system has been developed that can save operators more than 85% on their fuel costs by operating entirely on processed fuel gas straight from the field.

The technology not only saves operators money, but it also significantly reduces air emissions produced by the well completion process. The turbine power technology has already passed EPA Tier 4 emissions standards years ahead of the 2015 industry deadline. The system can fracture a well while producing zero particulate matter and nitrogen oxide emissions, two emissions that federal regulators have targeted in the Tier 4 standards.

In addition to the ability to use natural gas straight from the field, the technology offers operators the flexibility of using traditional No. 2 diesel, LNG, or compressed natural gas (CNG), depending on the drilling location and the available service infrastructure. Each fuel is individually capable of powering the turbine fracturing pumps; unlike most natural gas-powered solutions, the fuel is not blended in any capacity.

Last, the pumping systems enable operators to reduce the size of their well pad footprint, which is a key advantage to E&P companies working in mountainous regions where roads and topography present a tremendous challenge.

In these test results, Figure 1 is based on 500 hhp, and Figure 2 is based on 1,000 hhp.

The importance of breakthrough technologies

It is only because of ongoing technology breakthroughs that the oil and gas industry working in the Lower 48 has been able to continue to find and economically develop massive quantities of oil, natural gas, and gas liquids reserves that were previously too costly to develop or technically unproducible. Globally, companies are spending billions on R&D and are competing for the next important breakthrough that will not only advance well economics and productivity but also reduce the impact of oil and gas development and production on the environment.

This system’s most substantial differentiator is the ability to fuel fracturing equipment with multiple forms of natural gas. Natural gas offers not only important environmental value, but it also drastically reduces fuel costs for hydraulic fracturing. In addition, it provides an operational advantage by significantly reducing downtime between stages for refueling because the gas can be constantly fed into the turbines.

TABLE 1. Fuel cost comparisons were based on 900 fracturing stages and the amount of fuel consumed. (Figures courtesy of Green Field)

The cost savings of running on CNG are still being evaluated but are estimated to fall somewhere between LNG and field gas.

Table 1 outlines the fuel cost comparisons based on 900 fracturing stages and the amount of fuel consumed. (Note: Unit cost is based on the fuel cost average in 2012.)

Field gas test

In November 2012, Green Field became the first company to operate a turbine fracturing pump (TFP) on 100% field gas during a demonstration test in an active field in North Texas. The demonstration consisted of a TFP hooked into a sales gas pipeline fed by a producing well. The company achieved a high-pressure run of 8,500 psi-260 scf/minute and achieved a low-pressure run of 4,000 psi-203 scf/minute. When idling, the pump burned 109 scf/minute. The line pressure for the demonstration was 660 psi, with a minimum require- ment of 250 psi needed by the TFP. Figures 1 and 2 show the test results.

The field gas was introduced into the pump from a producing well located 33 m (100 ft) away. The gas flowed out through the pipe to a gas processing unit, where it was dehydrated and chilled to remove the liquids. Once dehydrated, a compressor pushed the dry gas into a pipeline, where it was hooked up with a flange connection to the gas conditioning unit (GCU). The operator on this location provided a gas analysis beforehand, and the operator set the gas supply around Green Field’s parameters to provide clean dry gas for the test.

The GCU was rigged up to the fracturing unit with a standard steel braided hose. The entire system was first purged with nitrogen and checked for leaks. The nitrogen was bled off, and the system was pressurized with natural gas. Finally, Green Field checked for leaks again and administered a sniffer test with a combustible detection meter to check for proper oxygen content and explosive limits.

Once pressurized with gas, the fracturing process was initiated. For this demonstration the source water was provided on site and stored in a 500-bbl frac tank. This water was charged to the TFP via a standard C pump. The pump was rigged up normally, and water flowed back into the same tank. Green Field used the choke to create horsepower and reached 8,500 psi – the standard pressure for a fracturing job – and ran full separate tests at 500 hhp and 1,000 hhp. Pressures and rates were sustained, and each test was successfully run for 20 minutes.

Tier 4 emission standards

TABLES 2 and 3. Turbine pumps emit 87% less NOx than conventional pumps and 77% less CO than the competition.

From an environmental standpoint, the cleaner, fuel-burning capability of this TFP is an advantage and differentiator to existing technologies.

In May 2004, the US Environmental Protection Agency signed the final rule introducing Tier 4 emission standards, which were to be phased in between 2008 and 2015. The Tier 4 standards require that emissions of particulate matter and nitrogen oxides be reduced by about 90%.

The new TFPs burn significantly cleaner than a conventional fracturing pump running on diesel, which traditionally has been used to power fracture stimulation jobs. These produce no emissions while running on natural gas. As a result, the technology already exceeds the EPA Tier 4 requirement without reducing hhp. As seen in Tables 2 and 3, when turbine pumps are compared with conventional pumps running on diesel, these TFPs emit 87% less nitrogen oxide and 77% less CO than the competition. This is of tremendous value in a region where environmental regulation and concerns are highly stressed.

In addition to the lower emissions benefits, another differentiator is the fact that these TFPs contain the highest power density on the market, thereby enabling operators to significantly reduce the size of the drilling pad footprint. This is a major benefit in regions where roads can be treacherous, pad space is limited due to the topography, and environmental regulation is stringent.